Crash and Burn - sadly you are displaying your total ingorance of the 744 in your rather ill advised post. For a start, from Glasgow to Manchester is not 'a few more tons of fuel' in a 747. Given you are very shortly about to start your descent it is probably about 2 tons max, if that. Your comment about the accuracy of the weather forecasts is also rubbish. Never heard of Satcom or ACARS? That crew had the 18 hr forecast for LHR when they left LAX, tied in with the sig wx charts and many years of personal experience. Throughout the flight they had access to METARS for LHR updated every 30 minutes plus the latest TAFs as they were issued. I doubt there was another crew on the North Atlantic that night who were better informed of the weather situation not just at LHR but LGW,BHX,MAN,SNN,PIK,GLA and KEF, plus a few more on the western side of the pond.
For your benefit, let me explain the fuel system of the 744 in very simple terms. When you get to the closing stage of the flight, you have four engines being fed directly by four associated tanks, each balanced with around 3.5T of fuel. Each tank feeds its engine. With number 2 engine out then the number 2 tank can feed the remaining three engines. It was only very late in the flight that it began to appear that the number 2 tank possibly was not working as it should and maybe the fuel might become unavailable, a conclusion reached when the tank contents bgean to reduce at a lower rate than the other tanks (nb the tanks had been working normally for the previous ten hours). At that point the crew took immediate action to divert. Not four hours earlier when everything was under control. Not one hour later when it would transpire the the fuel was usuable at all. They diverted and declared the mayday when the new problem presented itself. Very sensible decision.